Project Summary Understanding the basis of visual function may lead to the advancement of various fields, including behavioral biology, machine vision, blindness, and other neuropsychiatric disorders associated with visual symptomology, such as autism and schizophrenia1,2. Visual function in the brain occurs at multiple stages of processing: (1) sensation of raw visual input, (2) extraction of relevant features, and (3) determination of the appropriate behavioral output for accomplishing the goals of the organism. Structure and functional properties of retinal circuits responsible for sensing raw visual input have been thoroughly characterized3. Beginning in the 1960?s with Hubel and Wiesel?s work on cellular response properties of the primary visual cortex (V1), the field of visual neuroscience has made great strides in understanding the neural encoding of low-level visual features4,5. However, the mechanisms responsible for transducing visual input to behavioral output are poorly understood. This knowledge gap is the focus of this proposal. The mammalian visual brain is comprised of the subcortical pathway, which is highly conserved among vertebrates, and the more evolutionarily recent cortical pathways. Both cortical and subcortical pathways have access to raw visual input from the retina. The superior colliculus (SC) is a layered, subcortical structure of particular interest to visually guided behaviors; cells in the superficial layers exhibit sensory response properties similar to those in V1, while cellular activity in deeper layers is related to motor behavior6. Sensory-related cells in both the superficial SC and V1 are organized retinotopically and exhibit orientation selectivity, meaning they are strongly activated by visual stimuli presented in a preferred orientation but weakly activated by the null orientation. Interestingly, orientation preference of superficial SC cells is not evenly distributed across the visual field, implying a spatial bias in detecting oriented visual stimuli. There is no evidence for such a bias in the primary visual cortex (V1). This phenomenon marks a distinction between functional architectures of sensory cells in the SC and V17,8. The research described in this proposal exploits this functional distinction to determine the relative contributions of cortical and subcortical pathways to visually- guided behavior. The first aim of this proposal is to identify behavioral consequences of the SC?s functional architecture by assessing the spatial dependence of performance on a visual detection task. The second aim is to identify the extent of this architecture in superficial and deep SC layers by recording neural responses to oriented stimuli. The third and final aim establishes the role of cortical processes in guiding visual behavior by assessing behavioral performance in the absence of cortical influence. The results of this study will elucidate the subcortical and cortical contributions to processing visually-guided behavior.